The overall objective of this study is to characterize and define physiological and biochemical changes in hearts from animals subjected to stress, primarily that associated with exercise. The present goals follow naturally the findings to date. It is necessary to define what conditions foster the development of coronary collaterals. This will be done with pigs suffering either total or subtotal occlusion. Biochemical data show that wide variations exist between animals. Biopsies of heart and skeletal muscle before and after training will help solve the question of biochemical adaptation. More electron microscopic studies are needed before it can be resolved whether exercise affects the morphology of heart structure. Previous data on transmural flow changes following variations in total coronary flow, pressure, and resistance suggest that phasic wave forms of coronary flow may be indicative of transmural flow distribution. The hypertensive pig model will permit a more complete evaluation of this phenomenon. Finally, since coronary collaterals do not appear to increase following exercise, it is critical to measure maximum vascular volume and reserve.